1. Field of the Invention
The present invention relates to an expandable sand screen. More particularly the present invention relates to an expandable sand screen that permits fracturing of a hydrocarbon bearing formation after the well screen is expanded in a wellbore.
2. Description of Related Art
Hydrocarbon wells are typically formed with a central wellbore that is supported by steel casing. The casing lines the borehole in the earth and the annular area created between the casing and the borehole is filled with cement to further support and form the wellbore.
While some wells are produced by simply perforating the casing of the central wellbore and collecting the hydrocarbons, wells routinely include portions of wellbore that are left open or unlined with casing. Because they are left open, hydrocarbons in an adjacent formation migrate into these wellbores where they are affected along a perforated tubular or sand screen having apertures in its wall and some kind of filtering material to prevent sand and other particles from entering. The sand screen is attached to production tubing at an upper end and the hydrocarbons travel to the surface of the well via the tubing. In this specification xe2x80x9copenxe2x80x9d and xe2x80x9chorizontalxe2x80x9d wellbore refers to an unlined bore hole or wellbore.
Because open wellbores have no support provided along their walls, and because the formations accessed by these wellbores have a tendency to produce sand and particulate matter in quantities that hamper production along a sand screen, open wellbores are often treated by fracturing and packing. Fracturing a wellbore or formation means subjecting the walls of the wellbore and the formation to high pressure solids and/or fluids that are intended to penetrate the formation and stimulate its production by increasing and enlarging the fluid paths towards the wellbore. Packing a wellbore refers to a slurry of sand that is injected into an annular area between the sand screen and the walls of the wellbore to support the wellbore and provide additional filtering to the hydrocarbons. Fracturing and packing can be performed simultaneously. A cross-over tool is typically utilized to direct the fracturing/packing material towards the annulus of the open wellbore while returning fluid is circulated up the interior of the screen and returns to the surface of the well in an annular area of the central wellbore.
There are problems associated with the packing of an open wellbore. One such problem relates to sand bridges or obstructions which form in the annulus between the sand screen and the wall of the wellbore. These sand bridges can form anywhere along the wellbore and they prevent the flow of injected material as it travels along the annulus. The result is an incomplete fracturing/packing job that leaves some portion of the sand screen exposed to particulate matter and in some cases, high velocity particles that can damage the screen.
Today there exists a sand screen that can be expanded in the wellbore. This expandable sand screen xe2x80x9cESSxe2x80x9d consists of a perforated base pipe, woven filtering material and a protective, perforated outer shroud. Both the base pipe and the outer shroud are expandable and the woven filter is typically arranged over the base pipe in sheets that partially cover one another and slide across one another as the ESS is expanded. The foregoing arrangement of expandable sand screen is known in the art and is described in U.S. Pat. No. 5,901,789 which is incorporated by reference herein in its entirety. Expandable sand screen is expanded by a cone-shaped object urged along its inner bore or by an expander tool having radially outward extending rollers that are fluid powered from a tubular string. Using expander means like these, the ESS is subjected to outwardly radial forces that urge the walls of the ESS past their elastic limit, thereby increasing the inner and outer diameter of the ESS.
The biggest advantage to the use of expandable sand screen in an open wellbore like the one described herein is that once expanded, the annular area between the screen and the wellbore is mostly eliminated and with it the need for a gravel pack. Typically, the ESS is expanded to a point where its outer wall places a stress on the wall of the wellbore, thereby providing support to the walls of the wellbore to prevent dislocation of particles.
While the ESS removes the need for packing the wellbore with sand, it does not eliminate the need to fracture the formation in order to improve production. Fracturing prior to expanding the screen in the wellbore is not realistic because the particulate matter, like the sand used in the fracturing will remain in the annulus and hamper uniform expansion of the screen. Fracturing after expansion of the expandable sand screen is not possible because, as explained herein, the annular path for the fracturing material has been eliminated.
There is a need therefore for an expandable sand screen for use in a wellbore to be fractured. There is a further need for an expandable sand screen that can be expanded prior to the fracturing of the wellbore surrounding the screen. There is yet a further need for an expandable sand screen that forms a path or conduit for the flow of fracturing material along its outer surface after it has been expanded.
The present invention provides apparatus and methods for expanding an expandable sand screen in an open wellbore and then fracturing the wellbore. In one aspect of the invention, an expandable sand screen includes a perforated inner pipe and outer shroud. The outer shroud includes a plurality of longitudinal channels that retain their general shape after the expandable sand screen is expanded. In the expanded state, the channels provide a fluid conduit along an area between the screen and the wall of the wellbore. In a subsequent fracturing operation, a slurry travels along the conduits permitting communication of the slurry with hydrocarbon bearing formations to effectively fracture the formation. In another aspect, a method of fracturing includes expanding an expandable well screen in a wellbore whereby the expanded screen provides longitudinal channels in communication with the hydrocarbon bearing formation. Thereafter, fracturing slurry is injected and travels along the channels, thereby exposing the slurry to the formation. In yet another aspect of the invention, joints of the ESS are assembled together into sections and the channels on the outer surface of each joint are aligned to ensure that the longitudinal channels are aligned throughout the ESS section.